Cellulose acetate composition



Patented May 28, 1940 I UNITED STATES CELLULOSE ACETATE COMPOSITIONHerbert L. Wampner and Charles Bogin, Terre Haute, Ind.,' assignors toCommercial Solvents Corporation, Terre Haute, Ind., a corporation ofMaryland No Drawing.

Application August 14, 1933,

Serial No. 159,110

3 Claims.

Our invention relates to cellulose acetate compositions, andparticularly to such compositions comprising cellulose acetate, nitrosaturated nonbenzenoid hydrocarbons, and aliphatic alcohols.

While a great many satisfactory and readily available solvents have beensuggested for nitrocellulose, relatively few solvents are available forcellulose acetate, and most of these are unsuited for general use onaccount of such factors as low T tolerance for diluents, solubility inwater with resulting blushing tendencies, and especially unsatisfactoryrates of evaporation.

An object of our invention is to provide solvent components forcellulose acetate compositions i which have a wide range of evaporationrates and which have general application for at least partiallydissolving cellulose acetate. A further object of our'irivention is toprovide cellulose acetate solutions which are particularly suitable forcoating purposes, are free from blushing difficulties, and which may bevaried in composition to secure diiferent rates of evaporation, etc.Other objects and advantages of our invention will be apparent from thefollowing description.

The nitro non-benzenoid hydrocarbons containing 2 or more carbon atomsare not per se solvents for cellulose acetate. However, we have nowfound that when mixed with suitable proportions of monohydric aliphaticalcohols these nitro saturated non-benzenoid hydrocarbons are capable ofat least partially dissolving the various commercial grades of celluloseacetate, and that combinations of these nitroparafllns, especially thoseof 2 to 4 carbon atoms, with lower allphatic alcohols are excellentsolvents for the low acetyl grades of cellulose acetate commonlyemployed in coatingcompositions. Y

The nitro saturated non-benzenoid hydrocarbons which are suitable foruse in accordance with our invention constitute the nitroparaflinscontaining 2 or more carbon atoms and the cycloalkyl and arylsubstituted nitroparafllns. Among these-materials we prefer to employthe lower nitroparafllns such as nitroethane, 1'-nitropropane,2-nitropropane, l-nitrobutane, l-nitroisobutane, and mixtures of suchmaterials obtained by the nitration of saturated hydrocarbons.

Any monohydric aliphatic alcohol may be employed in our solvent mixturesbut we prefer to utilize the lower members of this series, e. g., al-

cohols containing from one to six carbon atoms.

As will be pointed out below, we prefer 'to' employ only the alcohols ofone to four carbon atoms in order, to secure clear solutions withcertain types of cellulose acetate. The particular alcohol to beemployed in any case will depend upon the -'other components of thecomposition and the results desired. Thus, if it is desired to deposit aclear film of cellulose acetate it will usually be necessary to includein the composition an alco- 5 ho] having an evaporation rate comparabletothe nitrohydrocarbon employed in order that the cellulose acetate maystay in solution throughout the evaporation of the solvents. If constantevaporating mixtures of any of the solvent components are formed, careshould be taken to provide a proper ratio of nitrohydrocarbons toalcohols at all stages of the evaporation. Mixtures of alcohols may befound desirable from this and other standpoints, and one skilled in theart may la readily determine by preliminary experiments the best alcoholor mixtures of alcohols for any given purpose.

Our invention is applicable to any of the commercial grades of celluloseacetate ranging from the low acetyl, low viscosity, grades to the highacetyl grades known as cellulose triacetate. These different grades ofcellulose acetate vary widely in solubility, the low acetyl grades, i.e., having acetyl numbers ranging from 36-38, being the most soluble,and the other grades decreasing in solubility with increase in theacetyl number. We have found that the solubility of the various gradesof cellulose acetate also decreases, in general, with increase in themolecular weight of the nitrohydrocarbon and increase in molecularweight of the aliphatic alcohol. Thus, the solubility varies over a widerange from complete solubility of the low acetyl grades of celluloseacetate in mixtures of lower nitroparamns and lower aliphatic alcohols,to only partial solubility of the high acetyl grades of celluloseacetate in mixtures of the higher nitroparafllns and higher aliphaticalcohols.

Although clear solutions may be obtained with high acetyl grades ofcellulose acetate in mixtures of the low molecularweight'nitrohydrocarbons of this group, and low molecular weightaliphatic alcohols, and clear solutions of the very low acetyl grades ofcellulose acetate may be obtained in mixtures of the higher molecularweight nitrohydrocarbons and aliphatic alcohols, we have found thatthere is a definite group of compounds within which complete solubilityoccurs with proper proportions of all combinations of 5 0 celluloseacetate, nitrohydrocarbons, and aliphatic 'alcohols.f This groupincludes the grades of cellulose acetate having acetyl numbers "below40, aliphatic alcohols containing from one to four carbon atoms, andnitroparaflins of the group consisting of nitroethane, l-nitropropane,2-nitropropane, l-nitrobutane, and l-nitroisobutane.

Although complete solubility, with resulting clear solutions, is secureduniformly only within the group defined above, it is to be understoodthat our invention is not limited to this particular range of materials,but is applicable generally to the use of mixtures of nitro saturatednonbenzenoid hydrocarbons of 2 or more carbon atoms and monohydricaliphatic alcohols for at least partially dissolving cellulose acetate.In the cases in which the material is not completely dissolved, thesolvent mixture serves as an excellent wetting and swelling agent, thusfacilitating complete solution of the cellulose acetate in subsequentlyadded solvents. In such cases our solvent mixtures are particularlydesirable, since in conjunction with other cellulose acetate solventsthey enable a considerable proportion of the relatively cheap aliphaticalcohols to be substituted for the more expensive active solvents. Insome cases of incomplete solution, completely or partially gelledliquids are obtained which may be used in any manner in which suchcompositions are employed in the art. It is to be understood, therefore,that our invention includes all such compositions as well as clearsolutions of cellulose acetate in the solvent mixtures.

In carrying out our invention the cellulose acetate is contacted withthe mixture of nitro saturated non-benzenoid hydrocarbon and monohydricaliphatic alcohol to secure at least partial solution of the celluloseacetate. In view of the physical form of the cellulose acetate, it isdesirable to agitate thoroughly-to effect as complete solution aspossible. In certain cases, particularly compositions including solventconstituents of relatively high molecular weight, it is desirable toapply heat to aid in securing maximum solution. The application of heatwill increase solubility in all cases, but after cooling to atmospherictemperature, some of the dissolved cellulose acetate may be thrown outof solution or the solution may subsequently gell unless a solventmixture properly formulated to secure complete solution is employed.

The proportion of aliphatic alcohol to be employed in the solventmixture will depend upon the nitrohydrocarbon and the alcohol utilized,upon the desired viscosity and flow characteristics, and upon thedesired degree of tolerance for hydrocarbon diluents. In each case adefinite minimum amount of alcohol is required to activate thenitrohydrocarbon, and this minimum amount increases with increasingmolecular weight of the nitrohydrocarbon and of the alcohol. Thus, 25%of ethyl alcohol, based on the volume of the total mixture, willactivate nitroethane sufficiently to dissolve low acetyl grades ofcellulose acetate; whereas approximately of secondary butyl alcohol isrequired to activate l-nitroisobutane sufliciently to dissolve celluloseacetate of medium acetyl grade. For each combination of nitrohydrocarbonand alcohol there is also an upper limit of alcohol content for maximumsolubility which decreases with increase in molecular weight. Thus, inthe case of nitroethane and ethyl alcohol the upper limit of the alcoholcontent is approximately 75% by volume of the total mixture, whereas inthe case of l-nitropropane and normal-butyl alcohol the upper limit ofthe alcohol content is approximately 60% of the total mixture. There isthus a range of proportions for maximum solubility which decreases inscope with increase in the molecular weight of the compounds.

As has previously been pointed out, other cellulose acetate solvents maybe utilized in conjunction with solvent mixtures, and a small proportionof an auxiliary slow evaporating solvent may be found desirable from thestandpoint of ease of formulation to insure complete solubilitythroughout the evaporation of the solvent mixture. Hydrocarbon diluentswhich are commonly employed in the art, such as benzol, toluol orpetroleum hydrocarbons, may also be incorporated in the solvent mixture,and there will be a tolerance range for each particular combinationemployed, the tolerance tending to decrease with increase in molecularweight of the alcohol and nitrohydrocarbon. The trend of the range ofcomposition of the solvent mixture may be seen from the above discussionand from the following specific examples, and one skilled in the art mayreadily determine by preliminary experiments a suitable composition forany particular purpose.

The following examples illustrate solutions of cellulose acetate in ourimproved solvent mixtures:

Example I A clear solution of cellulose acetate (acetyl number38.0-40.0; 20% A. S. T. M. viscosity 2.0-5.0) was prepared by dissolving10 parts by weight of this material in 100 parts by weight of thefollowing solvent mixture:

Per cent by volume Nitroethane Ethyl alcohol Example II A clear solutionof cellulose acetate (acetyl number 38.7-39.4; 20% A. S. T. M. viscosity70.0-140.0) was prepared by dissolving 4 parts by weight of thismaterial in 100 parts by weight of the following solvent mixture:

Per cent Nitrated propane Ethyl alcohol 35 n-Butyl alcohol 10 Nitromethane Nitroethane 26 l-nitropropane 32 2-nitropropane 33 ExampleIII A clear solution of cellulose acetate (acetyl number 40.1-40.5; 20%A. S. T. M. viscosity 18.0-23.0) was prepared by dissolving 6 parts byweight of this material in 100 parts by weight of the following solventmixture:

Per cent by volume l-nitroisobutane Sec. butyl alcohol 35 Example IV Aclear solution of cellulose acetate (acetyl number 37.0-38.5; 20% A. S.T. M. viscosity 1.8-4.5) suitable for use as a coating composition wasprepared by dissolving 10 parts by weight of the cellulose acetate in100 parts by weight of the following solvent mixture:

Per cent by volume Nitroethane 40 Ethyl alcohol 25 Toluol 35 Example V Aclear solution of cellulose acetate (acetyl number 37.0-38.5; 20% A. S.T. M. viscosity 1.8-4.5) suitable for use as a coating composition wasprepared by dissolving 10 parts by weight of the cellulose acetate in100 parts by weight of the following solvent mixture:

Per cent by volume l-nitropropane 35 Ethyl alcohol 25 n-Butyl alcohol 10Toluol 30 Example VI A clear solution of cellulose acetate (acetylnumber 38.7-39.4; 20% A. S. T. M. viscosity 2.5-5.0) suitable for useasa coating composition was prepared by dissolving 10 parts by weight ofthe cellulose acetate in 100 parts by weight of the following solventmixture:

Per cent by volume l-nitrobutane 50 n-Butyl alcohol 20 Toluol 20 Fuseloil amyl alcohols 10 positions for coating materials, for the deposition7 of films, or for other known uses in the art. Likewise, numerousequivalents may be employed for the materials specifically mentioned inthe examples, and, as has been previously pointed out, our invention isnot limited to the production of clear solutions but is applicablegenerally in at least partially dissolving cellulose acetate. It is tobe understood, therefore, that the use of any equivalents ormodifications of procedure which would naturally occur to one skilled inthe art is included within the scope of our invention.

Our invention now having been described, what we claim is:

1. A method of dissolving cellulose acetate of a grade having an acetylnumber below 40 to produce a clear solution which comprises contactingthe cellulose acetate with a mixture of a nitroparaffin chosen from thegroup consisting of nitroethane, l-nitropropane, Z-nitropropane,l-nitrobutane, and l-nitroisobutane, and a monohydric aliphatic alcoholcontaining from 1 to 4 carbon atoms.

2. A composition. of matter comprising cellulose acetate having anacetyl number below 40, and a solvent mixture comprising a nitroparaflinchosen from the group consisting of nitroethane, l-nitropropane,2-nitropropane, 'l-nitrobutane, and l-nitroisobutane, and a monohydricaliphatic alcohol containing from 1 to 4 carbon atoms, the components ofthe solvent mixture being in such proportion as to completely dissolvethe cellulose acetate.

3. A coating composition comprising cellulose acetate having an acetylnumber below 40, a nitroparaflin chosen from the group consisting ofnitroethane, l-nitropropane, 2-nitropropane, 1- nitrobutane, andl-nitroisobutane, a monohydric aliphatic alcohol containing from 1 to 4carbon atoms, and a hydrocarbon diluent, the solid and solventcomponents being of such character and in such relative amounts as tomaintain the cellulose acetate in solution during evaporation of thesolvent components to deposit a film.

HERBERT L. WAMPNER. CHARLES BOGIN.

